U.S. Pat. No. 3,592,106 describes a hydraulic piston-cylinder group. The cylinder is equipped with a channel in which a piston ring is located, positioned between the cylinder-piston sealing elements and the free end of the piston. The bottom of the channel affords a radial hole that places the channel in communication with the free end of the cylinder. The free end of the cylinder is subject to an overpressure that slows the motion of the cylinder when the cylinder is proximal to an end-run position and the piston ring moves beyond the outlet hole of the pressurized fluid that actuates the cylinder.
The end of the cylinder exhibits a further radial hole that puts the free end of the cylinder into communication with an annular chamber formed between the piston-cylinder sealing elements of known type and the piston ring. The further hole enables a controlled outflow of the fluid trapped in front of the free end of the piston towards the outlet hole.
The transit of fluid through the further passage generates a noise of the cylinder-piston group when in a deceleration step and proximal to the end-run position.